Furnace combustion control system



March 15, 1932,

F. D. POTTER FURNACE COMBUSTION CONTROL SYSTEI Filed Oct. 26, 1929 2 Sheets-Sheet 1 aq zq #21? QJJMW AT TORN EYS March 15, 1932., 1 D P T 1,849,638

FURNACE COMBUSTION CONTROL SYSTEM Filed Oct. 26, 1929 2 Sheets-Sheet 2 IN VEN TOR. fiea e/vcl D. ffer 7672 $125M m; V ATTORNEY Patented Mar. 15, 1932 UNITED STATES PATENT OFFKCE FREDERICK D. POTTER, OF LINDEN, NEW JERSEY, ASSIGNOR TO COMBUSTION CON- TROL COMPANY, INC., 0]? NEVT YORK, N. 1., A CORPORATION OF NE'iV YORK FURNACE COMBUSTIOH CONTROL SYSTEIVI Application filed October 26, 1929.

My invention relates to an improved meth- 0d and apparatus for controlling the combustion of fuel in a heat producing device such as the furnace of a steam boiler.

In the operation of a device of this character it is of the greatest importance for reasons of economy that the fuel be eillciently burned, which means that a minimum quantity of fuel be completely burned to produce CO substantially unmixed with CO, and that a desired high temperature be continuously and automatically maintained, notwithstanding variations in the rate at which the generated steam is being consumed.

My invention has for its object the accomplishing of the results aboveinentioned, and in its preferred embodiment I employ air feeding means, fuel feeding means, and means responsive to variations in the boiler steam pressure for varying the rate at which air and fuel are fed by said means. The air and fuel feeding means are preferably, although not necessarily, driven by electric motors.

At the beginning and before tae steam has reached the desired working pressure, the means responsive to steam pressure causes the air and fuel feeding means to so act as to deliver increased or maximum quantities of air and fuel to the furnace.

The desired working steam pressure is usually within a certain predetermined narrow zone or range of pressures, and whenever the steam pressure is within such zone, the fuel feed will preferably be operated at a constant rate, while the air feed will be controlled by means responsive to the temperature of the furnace or flue gases (or to the percentage of CO in such gases which corresponds to their temperature) and in case of a drop in temperature by means responsive to the percentage of CO in said gases.

l Vhenever the temperature or CO content is at or above a given value, the air feed will operate to supply a constant volume of air. In case the temperature orCO content falls below said given value, the rate at which air is supplied to the furnace will be varied by means responsive to the CO content of the furnace or flue gases, as follows:

Serial No. 402,685.

Assuming that the CO content is at or above a given value, thereby indicating that the low temperature is due to an insufficient air supply, the means responsive threto will cause air to be supplied at an increased rate; and in case the CO content is below said given value, indicating that the low temperature is due to an excessive air supply, said means will cause a diminution of the rate at which air is supplied to the furnace.

Whenever the steam pressure rises above said intermediate or working Zone, which it is the object of the invention to maintain, the means responsive to steam pressure causes the air and fuel feeding means to so act as to deliver diminished quantities of air and fuel to the furnace.

There is also by preference a stack damper and means responsive to the pressure of gases within the fire boX or combustion chamber for varying the extent of opening thereof, the damper being moved to increase the area of the flue passage as the pressure rises and vice versa to decrease such area as the pres sure falls. By such means the pressure may be maintained at a substantially constant and desirably low value, and damage to the furnace lining by the hot gases minimized.

Various details for facilitating and im proving the action of the control elements from the standpoint of reliability, durability and accuracy are also included within the invention, all as hereinafter set forth and claimed.

Reference is hereby made to the accompanying drawings, of which,

Fig. l is'a diagrammatical View of a control apparatus embodying my invention;

Fig. 2. is an enlarged section on the line 22 of Fig. 1;

Fig. 8 is a plan view of a switch device of Fig. 1; and

Fig. 4t is a side elevation of the same, partly broken away.

Referring to Fig. 1, 1 is a steamboiler furnace in which combustion is to be regulated and controlled in accordance with my invention. To this end I provide a steam pressure gauge 2 of standard type connected with the furnace boiler (not shown) and having an galvanometer til arm or needle 156 pivoted at 3a and movable about said pivot in response to variations in the boiler steam pressure, an increase of pressure causing movement of the needle in a clockwise direction, and a decrease of pressure causing movement in the opposite direction. I

The function of the needle 156 is to act as av switch arm for closing certain electric control circuits which will now be described.

The body of the gauge 2 occupies a horizontal position and is provided with a face of insulating material 182 having two arcuate troughs 134 and 186 filled with mercury, said troughs being concentric with respect to pivot 3a. The end of the needle is provided with an inverted U-shaped contact member 158 pivoted thereto on a horizontal axis in such position that the extremities of its depending arms are immersed in the mercury of the troughs 134 and 136.

Insulating partitions separate the troughs into several sections. In the outer trough there are two partitions separating said trough into three sections, a long section 140 and two shorter sections 142 and 144. In the inner trough there are two partitions separating said trough into three sections, a long section 150, one medium length section 152. and a short section 154.

The section 140 of the steam gauge corresponds to the lower range of pressure which prevails when the fire is being started or when steam has been used at an excessive rate. \Vhen the needle contact is in such section electric circuits are established as follows: from a low voltage (for example, six volts) line wire 7 through wire 200 and mercoid switch 120, thence to the mercury in section 150 of trough 136, thence through contact 158 to the mercury in section 140 of the outer trough 134, thence through wire 9 back to the line through two branch paths, for controlling respectively the fuel feed and the air supply, viz. (1) through relay 26 and wire 10 to line wire 11; and (2) through relay 36 and wire 12 to line wire 11.

The effect of the closing of branch circuit (1) is by the energizing of relay 26 to operate a switch 26 preferably of the mercoid type and thereby to close a circuit through solenoid 70 for operating any suitable means for increasing the rate at which fuel is supplied to the furnace, for example, a rheostat arm 7 9 by which a fuel feed electric motor 84 is speeded up.

The effect of the closing of branch circuit (2) is by the energizing of relay 36 to operate a switch 36 preferably of the mercoid type and thereby to close a circuit through solenoid 50 for operating any suitable means for increasing the rate at which air is supplied to the furnace, for example, a rheostat arm 60 by which an air feed electric motor 64 is speeded up. The effect of speeding up the fuel and air feed motors is to increase the rate of feed of fuel and air which increases the degree or amount of combustion in the furnace, thereby causing the boiler steam pressure to rise and the needle 156 to move in a clockwise direction. There are numerous equivalent means for varying the rate of feed of fuel and air, for example, gates or valves in fuel and air supply pipes controlled by solenoids or other electrical or electromagnetic devices, or steam engines for driving feed devices and having throttles similarly controlled.

In order that the action of the mercoid 120 and solenoids 70 and 50 above referred to may be more fully understood, I shall now describe their mode of operation and then return to a description of the steps which occur as the needle 156 continues its movement.

The mercoid 120 together with another mercoid 122 is mounted on a tilting beam 118 which is pivoted on a horizontal pivot 124 and normally rests upon a stop pin 126 as shown. In this position both mercoids are open circuitcd and no current can flow. A vertical arm 116 rigid with the beam 118 extends up wardly therefrom in position to be contacted and moved by one of the pins 114 of a timing device, and which as shown comprises a disk 115 mounted on a horizontal shaft 112 and having its periphery formed with ratchet teeth 110.

The disk 115 is continuously driven with a step by step movement whenever the furnace control system is in operation. The driving means comprises an electron'iagnet 30 intermittently energized as follows: An electric circuit is established from a line wire 31 of suitable voltage, for example 110 volts, through service switch and mercoid 18, thence through the coil of magnet 30, thence in series through the coils of three relays 12, 14 and 16 to line wire 32.

The mercoid is normally closed as shown. It is supported on a beam 41 which is pivoted on a fixed horizontal pivot 19. The beam 41 is rigid with the magnet armature 21 which is normally held against a. stop pin 25 by a coil spring 23.

When the magnet is energized by the closing of the circuit above described, the armature is drawn toward the right thereby causing its pivotal pawl 27 to advance the disk 115 the distance of one ratchet tooth. At the same time the beam 41 is tilted sufficiently to cause the mercoid 18 to open the energizing circuit, whereupon the magnet releases armature 21 and the spring thereupon returns it to the position shown, whereupon the mercoid 18 again closes the circuit and the sequence of operations is repeated.

The current which energizes the relays 12,

4 and 16 is therefore an intermittent or pul sating current and causes each relay to intermittently open a normally closed mercoid switch designated respectively as 12, 14 and 16. i

The apparatus above described for imparting a step by step movement to the disk 115 and for energizing the relays 12, 14 and 16 is merely one form which may be employed, and it should be understood that many other devices, preferably of an electro-mechanical nature, may be substituted therefor.

The intermittent opening and closing of mercoid 12 together with the energizing of relays 26 and 36 as previously described sets up intermittent currents through the solenoids 0 and which thereupon impart a step by step movement in a clockwise direction to the ratchet wheels 80 and 61 and rheostat arms 7 9 and by the action of cores 74 and 54 and pawls 7 8 and 58. Such movements out out resistances 82 and 62 and increase the speed of the motors 84 and 64.

It should be. borne inmind, however, that although the relay 12 is always in action so long as switch 20 is closed, the circuits controlled by its mercoid 12 can be closed only when the mercoids 26 and 36 are closed by the action of relays 26 and 36 and such relays are energized only when current is passed by one of the mercoids 120 and 122 of the timing device. In other words, in operating my system, I prefer that the various controls actuated by needle 156 of the steam gauge shall not be active all of the time, but only a part of the time at regular intervals, and that the length of the time interval during which the control is active shall vary according to the position of said needle which sometimes completes a circuit through mercoid 120 and at other times through mercoid 122 the time interval of which is different, as will be shown. 7

In the normal position of the beam 118, in which it rests on pin 126, as shown, mercoid 126 is closer to a horizontal position than in rccid 122. On this account, as the beam is tilted by engagement of pin 114 with arm 116 mercoid 120 will close its circuit sooner than mercoid and the time interval for the closed circuit will be correspondingly longer than that of mercoid 122; for example, the time interval for mercoid 122 may be one or more seconds and that for mercoid 120sevoral times as long. Each of such intervals is separated by an interval during which the mercoids are in open circuit position and the control. elements are therefore inactive. The intervals of open circuit are preferably, although not necessarily, longer than the greatest interval of closed circuit.

Returning to the action of the steam gauge needle 156, as the steam pressure increases the needle moves in a clockwise direction until the contact 158 leaves section 150 of groove 136 and enters section 152. The last named section is connected with line wire? through mercoid 122 instead of mercoid 120 and the results produced are the same as before except that the time intervals for the activity of the control elements are shortened and the intervals ofrinactivity correspondingly lengthened.

I The next change occurs when the needle contact 158 enters section 142 of groove 140. This position or zone corresponds to the zone or range of steam pressure which it is desired to maintain in the boiler, that is, the working steam pressure. While the needle contact is in section 142 no variation in the rate of fuel feed takes place. The rate at which air is fed to the furnace is controlled primarily by the CO content or temperature of the furnace and secondarily by the CO content thereof, whereby the combustion is stabilized and maintained in a condition of highest efliciency.

In case the temperature is at or above a desirably high value, which means that the CO content is high, the circuits for causing a variation in the rate of the air supply are open at mercoid 40 and air will be supplied to the furnace at a constant rate, irrespective of the CO content, but whenever the CO content and temperature fall below said value the rate at which air is fed to the furnace will be varied by means responsive to CO content.

In case the CO content is above a predetermined value, indicating that the temperature drop was due to an insuflicient air supply, the rheostat arm 60 will be operated to speed up the air feed motor. On the other hand, if the CO content is below said value,

indicating that the temperature drop was due to an excessive air supply, the arm 60 will be operated to diminish the air supply. These movements are brought about by the following means:

A wire 13 connects the trough section 142 with the energizing coil of relay 245', the circuit back to line wire 11 being completed through wire 15. The relay 245 is shown in Figs. 3 and 4. It comprises the usual energizing coil which receives current through wires 17 and 19 connected respectively to wires 13 and 15.

The core 243 of the magnet is connected by a link 243 with one end of a lever 238. This lever is secured to a block 238 which is rigid with a shaft 237, and the latter is mounted on centering screws or pivots 239. Upon the free end of the lever 238 is a weight 2238 of sulficient mass to normally hold the lever 238 against the stop 261 so that the magnet core 243 is partly withdrawn from the energizing coil.

There is a horizontal U-shaped frame 241 the ends of which are secured to blocks 235 rigid with shaft 237 and the cross bar 241 is so situated as to engage the end of the inclicator needle 233 of galva-nometer 263 when the needle is in the position shown.

The needle 233 is secured to a vertical pivot 233 so as to swing in a horizontal plane in response to variations in the CO content of the furnace gas. The apparatus for causing such movements is shown in Fig. 1.

There is a suction fan or blower 242 driven at suitable intervals by an electric motor (not shown) which is intermittently energized and deenergized by the line wires 7 and 11 through wire 21, wire 23, mercoid switch 278 and wire 25. The duration of the period of energization is determined by the mercoid 278 which is mounted on a bar 274 and caused to tilt on a horizontal pivot 275 by the action of the cam wheel 266. The latter element is mounted to rotate on a horizontal axis and is formed with three cam members 264 which are engaged in succession by the pin 268 carried by the timing disk 115. Each of such engagements which of course occurs only once per revolution. of said disk causes'a tilting of the beam 271- by reason of the engagement of one of the cams 264 with a pin 270 carried by the arm 27 which is rigid with said beam. The motor circuit is closed by such movement of beam 274 and remains closed until pin 268 has passed the cam 264 whereupon by gravity the mercoid 278 resumes the position shown, thereby opening the motor circuit.

During the interval in which the motor circuit is closed, the suction fan 242 rotates and draws furnace gas from the base of the stack through pipe 240 and delivers it to sealed chamber 246 which contains caustic soda. The CO in the gas unites with the caustic soda, leaving a mixture of air and CO. This mixture makes its exit from said chamber through the pipe 248 and passes through a tube 252 of insulating mate 'ial within which is a coil 250 of nickel wire. This coil is in series with a resistance coil 254 disposed upon the exterior of said tube, across line wires 7 and 11, as shown.

There is a similar coil 258 of nickel wire within an insulating tube 256 which is open to the atmosphere at both ends and said coil 258 is in series with a resistance coil 260 on the exterior of tube 256, across line wires 7 and 11.

The coils 250, 254, 258 and 260, together with the galvanometcr 262, form a Wheatstone bridge in which the resistances of coils and 260 are equal, and the resistances of coils 250 and 258 when surrounded by the same kind of gas are also equal. The galvanometer is connected between the junction of coils 250 and 254 and the junction of coils 258 and 260. The coils 250 and. 258 are heated by the current passing therethrough and their relative resistances will be altered by the fact that the mixture in contact with the coil 250 contains CO as well as air. This change of resistance causes a flow of current through the galvanometer 262 the strength of which is approximately proportional to the percentage of CO in the gas mixture.

Such current strength is indicated by the deflection of the needle 233. Such movements of the needle may if desired be recorded in any well known manner.

The presence of asubstantial percentage of CO in the furnace gas is undesirable since it means incomplete combustion of the fuel and a loss of heat units. Consequently the needle 233 is so mounted that a slight deflection thereof will bring its extremity above a later ally adjustable beam 247 as shown in Fig. 3. In this position the descent of the bar 241 caused by the energizing of the relay 245 effects the closing of a circuit by the following instrumentalities.

The beam 247, having an interior screw thread, is mounted upon a horizontal threaded support 253 so as to turn freely thereon. One end of said beam is provided with a stop 251 which normally rests upon the frame 231. The opposite end of the beam 247 is provided with a depending contact 249 adapted to enter the mercury in cup 257 which is supported by insulator 259 carried by frame 231.

The needle 233 is flexible and in a certain position corresponding to a definite percentage of CO in the furnace gas, will be above the beam 247. In such position the cross-bar 241 as it descends engages the needle 233 and flexes it, so that it engages the beam 247 turning it on its pivot and causing contact 249 to enter the mercury in cup 257.

The beam 247 may be adjusted laterally upon the support 253 so that it will be in position to be depressed by the needle 233 when the latter is at any desired position.

The movement just described completes a circuit from wire 13 through screw 253, beam 247, mercury cup 257, wire 27 and the energizing coils of two relays 22, 24 (Fig. 1) in multiple, to line wire 11.

The effect of energizing the relay 22 is to open a circuit at mercoid contact 22 to prevent the energizing of the solenoid 52 of the air feed control through the mercoids 32, 14 and The effect of energizing the relay 24 is to close at mercoid contact 24 a circuit which intermittently energizes the solenoid of the air feed control and causes the speeding up of the air feed motor. The effect of this is to increase the quantity of air fed to the furnace thereby securing more complete combustion, lowering the percentage of CO in the furnace gas, and increasing the temperature of the furnace gas. The circuit referred to includes the following mercoid contacts, viz., 32, 14, 40 and 24.

On the other hand, assuming that the temperature and CO content of the furnace gas are undesirably low, due to the supplying to the furnace of an excessive quantity of air, the CO content will be so low that the galvanometer needle will not be in position to actuate the beam 248,, and in such event neither of the relays 22 or 24 will be energized. In this event, a circuit will be completed through air feed solenoid 52 as follows: From line wire 32 through wire through mercoids 32', 14', and 22, to solenoid 52, thence to line wire 31, the mercoid 32 being held in closed circuit position by its relay 32 which is energized by its connection with wire 13 and line wire 11.

The solenoid 52 is thereby intermittently energized and by a step by step movement moves the rheostat arm in the proper direction for slowing up the air feed motor 64 and thereby diminishes the air supply. The result is to bring about more eflicient combustion in the furnace and raise the temperature of the furnace gas.

The means responsive to temperature or CO content of the furnace gases will now be described, it being understood that high temperature corresponds to a high CO content.

There is a thermocouple 230 mounted in the wall of the furnace l and connected by suitable wiring with a galvanometer 229 similar to galvanometer 262 and having a needle 233 similar to a needle 233 previously described, said needle 233 being similarly mounted in connection with a relay 245, and a laterally adjustable beam, the same as the beam 247. The current in the galvanometer circuit generated by the thermocouple 230 and the deflection of needle 233 caused thereby are proportional to the temperature or CO; content of the furnace gas. Whenever this factor reaches a predetermined value which may be varied by the lateral adjustment of the beam above referred to, the needle will by reason of the energization of relay 245 by wires 13 and 15 cause the closing 2* of a circuit through mercury cup 257 (similar to cup 257) as follows: 1

From trough section 142 through wire 13 to mercury cup 257, thence by wire 65 to energizing coil of relay 40 to line wire 11.

The effect of such energization of relay 40 is to open at merco-id contact 40' the circuits previously referred to in describing the means responsive to CO content, thereby making it impossible for the speed control of the air feed motor to be operated. Hence the motor will continue to run at a given speed.

In other Words, if the temperature and CO content are of a predetermined desired value the air feed motor must continue to run at a fixed speed since neither of the solenoids 50 and 52 can be energized, but if the temperature drops below such value the air feed motor speed will be increased if the CO percentage is above or decreased if the CO percentage is below a predetermined value.

7 The next position of the steam gauge needle 156 and which indicates a steam pressure higher thanis desired brings its contact 158 into section 144 of the outer trough 134 and connects the wire 220 with line wire 7 through inner trough section 152 and mercoid 122, (or, as the steam pressure increases, through inner trough section 154 and mercoid 120).

The energizing of wire 220 closes circuits in multiple through the energizing coils of relays 28 and 38. The energizing of relay 28 closes a circuit at mercoid contact 28 which also includes mercoid contacts 30 and 12' and the energizing coil of solenoid 72 of the fuel feed control, causing an intermittent energizing of the solenoid and by a step by step movement of the rheostat arm 79 a slowing up. or stopping of the fuel feed motor.

The energizing of relay 38 closes a circuit at mercoid contact 38', which also includes mercoids 30' and 12 and the energizing coil of solenoid 52 of the air feed control, causing an intermittent energizing of the solenoid, and by a step by step movement of the rheostat arm 60 a slowing up or stopping of the air feed motor.

The control system also includes a stack damper 102 and means for opening or closing same, ach means being responsive to the pressure of the furnace gas, as follows A pipe 162, having an open end 160 within the furnace combustion chamber, extends upward to a bell 164 partially submerged in li uid and serving to actuate a lever 166 pivote on a horizontal pivot 168. When the pressure is low the bell descends, thereby causing the long end of the lever to move downward until the contact 172 enters the mercury in a mercury cup 176. This closes a circuit from line wire 7 through said cup, thence through Wire 17 3 and the energizing coil of relay 42 to line wire 11.

The effect of the energizing of relay 42 is the closing of a circuit through solenoid 90 and the intermittent energizing of the same for effecting the closing or partial closingof the damper 102 by means of core 94, arm 98 and ratchet wheel 101. Said circuit is as follows: from line wire 32 through mercoids 16 and 42 to solenoid 90, thence by wires 95 and 97 to line wire 31.

The opening of the damper is effected by a rise of pressure in the furnace chamber sufficient to cause the bell 164 to raise the long end of lever 166 thereby depressing the short end thereof sufficiently to cause the contact 170 to enter the mercury in mercury cup 174. A circuit is thereby closed from line wire 7 through mercury cup 174 and energizing coil of relay 34 to line wire 11.

The effect of the energizing of relay 34 is the closing of a circuit through solenoid 92 and the intermittent energizing of the same for opening the damper by means of core 96, arm 100 and ratchet wheel 101. Said circuit is as follows: from line wire 32 through mercoids 16 and 34 to solenoid 92, thence by wires 99 and 97 to line wire 31.

By the means described the gas pressure within the fire box of the furnace can be very closely regulated and held at a desirably low value, whereby the destructive action of the furnace gas upon the lining is minimized.

The operation of the system is briefly as fellows Assuming the fire to have been start ed in the furnace and the steam pressure low, the steam gauge needle 156 by connecting inner groove section 150 with outer groove section 140 will cause the speeding up of both the fuel and air feed motors. This promotes the combustion of an increased quantity of fuel and increases the steam pressure. The needle therefore moves into section 152 of the inner groove and connects it witn section 140 of the outer groove. The only effect of this change of position is to substitute the mercoid 122 for the mercoid 120 of the timing device so that the control elements will be energized for shorter periods and at more Widely separated intervals. This is advantageous because the needle is now very close to the desired operating position, correspond ing to the steam pressure which it is desired to maintain in the boiler.

The steam pressure now rises sufficiently to carry the needle 156 from section 140 to section 142 of the outer trough. This effects a very important change of control. The steam pressure is now at the value which it is desired to maintain, and the control is now practically taken away from the steam pressure and is vested in the means responsive to temperature or CO content and CO content of the furnace gas. Such control, however, preferably relates only to the air supply and does not extend to the fuel supply which remains constant.

As long as the temperature of the furnace gas remains high the air feed motor continues to run at a constant speed.

In case temperature becomes unduly low from an excessive air supply, the CO percentage being also low for the salne reason, the air supply motor is slowed down. This reduces the air supply and causes the temperature to rise.

If the low temperature is accompanied by a high percentage of G0, which indicates an insufiicient air supply, the air feed motor is caused to speed up. This increases the air supply, improves combustion efficiency by causing more of the fuel to burn to CO instead of CO, and causes the temperature to rise.

The elements described will ordinarily hold the needle in the position last described over long periods of time and with considerable variation in the rate at which steam is consumed. In the event the needle drops back into section 1 10, the control elements will act as previously set forth to bring it into section 142. And in case the steam pressure r ses further and moves the needle intO section 144 the control elements will act by the slowing down of the fuel feed motor and air feed motor to cause the steam pressure to fall sufficiently to bring the needle back into section 142.

The term furnace gas as used herein refers to the mixture of hot gases within the combustion chamber or stack of the furnace which mixture includes air and products of combustion.

Having now described my invention, I claim:

1. A furnace, means for supplying air thereto to support combustion, means responsive to the presence of carbon monoxide in the furnace gas for controlling said air supply means, means for supplying furnace gas to said responsive means, and timing means for causing said furnace gas supplying means to be periodically actuated.

2. The combination of means for generating steam including a furnace, means responsive to the steam pressure while the steam is being generated and consumed for regulating the air and fuel supply of the furnace so as to increase the same when the steam pressure is below a predetermined minimum and decrease the same when the pressure exceeds a predetermined maximum, with an intermediate zone of pressure therebetween in which the fuel and air flow are unaffected by pressure changes, and means for regulating the air supply when the pressure is within the intermediate zone including means responsive to CO content of furnace gases for varying the air supply and also means responsive to the temperature of the furnace gases for maintaining a constant air supply.

3. The combination of means for generating steam comprising a furnace, means responsive to pressure of the generated steam for increasing the air and fuel supply of the furnace, means responsive to a higher steam pressure for decreasing the air and fuel supply, and means operative when the pressure of the steam is intermediate the pressures mentioned to increase the air supply when temperature in the furnace is low and the CO content of the furnace gas is high.

4. The combination of means for generating steam comprising a furnace, means responsive to pressure of the generated steam for increasing the air and fuel supply of the furnace, means responsive to a higher steam pressure for decreasing the air and fuel supply, and means operative when the pressure of the steam is intermediate the pressures mentioned to decrease the air supply when temperature in the furnace is low and the CO content of the furnace gas is low.

5. The combination of means for generating steam comprising a furnace, means responsive to pressure of the generated steam for increasing the air and fuel supply of the furnace, means responsive to a higher steam pressure for decreasing the air and fuel supply, and means operative when the pressure of the steam is intermediate the pressures mentioned to maintain a supply of air at a substantially fixed rate when the temperature in the furnace is high Without regard to the CO content of the furnace gas.

6. The method of controlling combustion in a steam generating furnace which comprises applying the pressure of the generated steam when below a predetermined value to increase the rate at which air and fuel are supplied, applying such pressure when above a predetermined value to decrease the rate at which air and fuel are supplied, and when such pressure is between said values causing an increases of rate of air supply when the furnace temperature is low and the CO content of the furnace gas is high.

7. The method of controlling combustion in a steam generating furnace which comprises applying the pressure of the generated steam when below a predetermined value to increase the rate at which air and fuel are supplied, applying such pressure when above a predetermined value to decrease the rate at which air and fuel are supplied, and when such pressure is between said values causing a decrease of rate of air supply when the furnaee temperature is low and the CO content of the furnace gas is low.

8. The method of controlling combustion in a steam generating furnace which comprises applying the pressure of the generated steam when below a predetermined value to increase the rate at which air and fuel are supplied, applying such pressure when above a predetermined value to decrease the rate at which air and fuel are supplied, and when such pressure is between said values causing air to be supplied at a substantially constant rate when the furnace temperature is high.

In testimony whereof, I have signed my name hereto.

FREDERICK D. POTTER. 

